This invention relates to a simplified process for the preparation of relatively high molecular weight polyamines in which the starting materials react at least partly to undergo urethane linkage and isocyanate groups are saponified to NH.sub.2 groups either at the same time and/or subsequently. The present invention also relates to relatively high molecular weight polyamino compounds prepared by this process.
Processes in which the amino groups of polyamines are formed from isocyanate groups of polyisocyanates or preformed isocyanate prepolymers are known to those skilled in the art. For example, it is known that aromatic isocyanates may be converted into primary aromatic amines by acid hydrolysis. However, the amine formed as a result of hydrolysis continues to react with unreacted isocyanate to form the corresponding urea. This secondary reaction cannot be suppressed even by using an excess of strong mineral acid. A comparatively recent example of this procedure is found in Japanese Pat. No. 55 007-827.
Acid hydrolysis of aliphatic monomeric isocyanates with dimethylsulfoxide/hydrochloric acid to form amines was disclosed by Walker and Pinches in "Analyst", 104, 928-936 (1979) as a method of detecting the presence of aliphatic isocyanates. In this process, the amines are derived from the corresponding modified or unmodified isocyanates or prepolymers (for example hexamethylenediamine obtained from biuretized hexamethylene diisocyanate) and their concentration is determined photometrically.
DE-B No. 1 270 046 discloses a process for the preparation of particular primary aromatic amines containing polyalkylene glycol ether segments, in which reaction products of aromatic di- or triisocyanates and polyalkylene glycol ethers and/or polyalkylene glycol thioethers (preferably those having molecular weights from 400 to 4000) are reacted with secondary or tertiary carbinols and subsequently (optionally in the presence of acid catalysts) subjected to thermal decomposition at high temperatures in an inert solvent. This process is disadvantageous in that high decomposition temperatures are required and the thermal decomposition of the urethanes is accompanied by the formation of combustible, readily volatile alkenes which form explosive mixtures with air. Special precautions are therefore required.
DE-B No. 1 694 152 discloses the preparation of prepolymers containing at least two amino end groups by reacting excess quantities of hydrazine, aminophenylethylamine or other diamines with an isocyanate prepolymer obtained from a polyether polyol and polyisocyanate (NCO:NH ratio=1:1.5 to 1:5). Any unreacted amine must be carefully removed in a subsequent step because the amine acts as both a reactant and a powerful catalyst for the reaction with polyisocyanates and thus causes shortened processing times.
Another possible method for synthesizing polyamines containing urethane groups has been described in French Patent No. 1,415,317. In this disclosed process, isocyanate prepolymers containing urethane groups are reacted with formic acid to form N-formyl derivatives which are saponified to terminal aromatic amines.
The reaction of isocyanate prepolymers with sulfamic acid according to DE-B No. 1,155,907 results in compounds having amino end groups. Relatively high molecular weight prepolymers containing aliphatic, secondary and primary amino groups are obtained, according to DE-B No. 1,215,373, by the reaction of relatively high molecular weight hydroxyl compounds with ammonia in the presence of catalysts under pressure and at high temperatures. Such high molecular weight prepolymers may also be obtained according to U.S. Pat. No. 3,044,989 or DE-B No. 1,193,671 by the reaction of relatively high molecular weight polyhydroxyl compounds with acrylonitrile followed by catalytic hydrogenation. Polyoxyalkylene polyamines may be produced according to U.S. Pat. No. 3,236,895 by amination with ammonia of sulfonic acid esters of polypropylene glycol. The reaction of a polyalkylene glycol with epichlorohydrin followed by a reaction with an excess of a primary amine to obtain products having secondary amino groups has been disclosed in French Patent No. 1,466,708. According to DE-A No. 2,546,536 and U.S. Pat. No. 3,865,791, relatively high molecular weight compounds having terminal amino groups and urethane groups may be obtained by reacting isocyanate prepolymers with hydroxyl group-containing enamines, aldimines or ketimines and then hydrolyzing the product. Another possibility of synthesizing aromatic polyamines containing urethane and ether groups lies in the ring opening which occurs in the reaction between isatoic acid anhydride and diols. Such polyamines have been described, for example, in U.S. Pat. No. 4,180,644 and DE-A Nos. 2,019,432; 2,619,840; 2,648,774 and 2,648,825. One disadvantage of such processes is the low reactivity of aromatic ester amines obtained.
The reaction of nitroarylisocyanates with polyols followed by reduction of the nitro groups to aromatic amino groups is also known (see U.S. Pat. No. 2,888,439).
Polyamines may also be prepared by the reaction of benzyl alcohol with isocyanate compounds having aliphatic or aromatic isocyanate groups to form benzylurethanes which are subsequently catalytically hydrogenated (DE-A No. 3,035,639). One major disadvantage of both these processes is the high cost of the reduction step carried out under pressure.
It is also known that certain heteroaromatic isocyanic acid esters may be converted into heteroaromatic amines by alkaline hydrolysis. The conditions of hydrolysis mentioned in H. John, J. Prakt. Chem. 130, 314 et seq and 332 et seq (1931) for two quite specific heteroaromatic monoisocyanic acid esters are however completely unsuitable for the conversion of polyisocyanate compounds into aliphatic and/or aromatic amines and also dangerous.
Another possible method for alkaline hydrolysis of isocyanate groups is disclosed in N. V. Sidgwick, The Organic Chemistry of Nitrogen, Clarendon Press, Oxford, 1966, page 236. This disclosure is however very general.
Various proposals disclosed in DE-A Nos. 2,948,419; 3,039,600 and 3,112,118 are multistage processes for the preparation of polyamines by alkaline hydrolysis of isocyanate prepolymers to carbamates. The hydrolysis is carried out at low temperatures using aqueous alkali metal hydroxide. The hydrolyzed mixture is then acidified with mineral acids or acid ion exchange resins in quantities equivalent to or in excess of the quantity of base and CO.sub.2 is given off. The mixture may then be neutralized and the product polyamines isolated therefrom. The carbamates may also be directly decomposed by heat to give rise to the polyamines without addition of acid.
The processes described above for the preparation of polyamines involve considerable expense. Even in the more simplified processes using prepolymers for the conversion of polyisocyanates into polyamines, a further simplification would be economically desirable. Since the isocyanate prepolymers must first be prepared from polyols and monomeric polyisocyanates before they are hydrolyzed and a major portion of the cost of such processes lies in the preparation, storage and handling of the isocyanate prepolymer, it would be advantageous to have a simplified process for producing polyamines which process does not require a prepolymer as the starting material.